Started dating a guy who was a swinger prior to our relationship...?

He had told me that he was pretty promiscuous prior to meeting me. Shortly after we started dating we discussed being monogamous, and both agreed that is what we want. He is a great man, and is incredibly sweet and thoughtful. He stays with me almost every night, cooks me dinner, we go out to fun places...he's great! However, We've been dating for a few months now, and we have only been intimate twice. It's been about a month ago, and I'm just curious as to what is going on? He was running around crazy before and now it's like he doesn't have an interest in being physical. He's affectionate, but I don't understand how he went from one extreme to the other. I asked him what's wrong and he says he's just been running himself ragged lately, and he's under a lot of stress. What can I do to ease the tension and hopefully spice things up?